NEURAL REPRESENTATION OF OBJECTS IN SPACE - A DUAL CODING ACCOUNT

I present evidence on the nature of object coding in the brain and dis cuss the implications of this coding for models of visual selective at tention. Neuropsychological studies of task-based constraints on: (ij visual neglect; and (ii) reading and counting, reveal the existence of parallel forms of spatial representation for objects: within-object r epresentations, where elements are coded as parts of objects, and betw een-object representations, where elements are coded as independent ob jects. Aside from these spatial codes for objects, however, the coding of visual space is limited. We are extremely poor at remembering smal l spatial displacements across eye movements, indicating (at best) imp overished coding of spatial position per se. Also, effects of element separation on spatial extinction can be eliminated by filling the spac e with an occluding abject, indicating that spatial effects on visual selection are moderated by object coding. Overall, there are separate limits on visual processing reflecting: (i) the competition to code pa rts within objects; iii) the small number of independent objects that can be coded in parallel; and (iii) task-based selection of whether wi thin- or between-object codes determine behaviour. Between-object codi ng may be linked to the dorsal visual system while parallel coding of parts within objects takes place in the ventral system, although there may additionally be some dorsal involvement either when attention mus t be shifted within objects or when explicit spatial coding of parts i s necessary for object identification.